The present invention is characterized by a combination of vapor-to-mechanical energy converters driven by rapid heat transfer means able to instantaneously transfer energy from the products of combustion, or any heat source, to a thermodynamic fluid circulating inside an independent loop. This fluid moves inside the loop mainly as a result of its own expansion and transfers its energy to mechanical means through thermodynamic work-producing units or expanders. In this manner, the various components of this device constitute a special Miniaturized Waste Heat Engine (MWHE) able to recuperate and convert waste energy from combustion or heat sources into useful energy. By returning a significant fraction of this recuperated energy to the power system (for example in the form of mechanical or electrical energy), the usually unavoidable heat discharge into the environment is minimized, while pollutant emission can be significantly reduced at no energy cost for the power system.
To simplify the description of the working principles and methods of operation of this invention, an internal combustion engine (fueled with heavy or non-heavy fuels) is from now on considered to be the power system. However, any power system utilizing heat sources and producing waste heat as a result of their operation could utilize the techniques and methods described by this invention.
When this invention is applied to an internal combustion engine, the energy of the exhaust combustion gases (high temperature and mass flow rate) is converted into additional horsepower transferred directly to the engine load, via the engine crankshaft, and/or indirectly via special engine intake oxygen enhancing means.
The MWHE contains one or more vapor-to-mechanical energy converting systems, referred to hereafter as expanders; one or more instantaneous heat transfer systems, referred to hereafter as converters; one or more instantaneous vapor collapsing systems, referred to hereafter as imploders; and one or more air/oxygen enhancing systems, referred to hereafter as oxygenators.
In general the MWHE is formed by one or more converters coupled with a series of expanders including a vapor condensing system, or imploder, so as to form a thermodynamic cycle A converter (or multiple converters) returns the recuperated energy from the exhaust gases through one or more expanders in the form of mechanical energy, adding it to the power normally generated by the engine. Another converter (or the excess recuperated energy of a single converter) allows the pressurization of the engine intake manifold through the oxygenator, thereby providing excess oxygen to the air fuel mixture independently of the engine rotational speed, or revolutions per minute (RpM). By utilizing this particular oxygen enhancing feature, the engine performance can be significantly improved since air/oxygen is virtually pumped into the engine at all times, regardless of the RpM, at no cost. If this device is applied to a diesel fuel engine, the production of highly toxic particulate is almost eliminated since excess oxygen is always present during combustion, even when the engine is accelerating from idling speeds.
Therefore, the main application of this thermodynamic engine can be seen as an anti-pollution system, especially when applied to heavy fueled engines but also as a device able to significantly improve engine performance while reducing fuel consumption. Again, it is important to emphasize that the source of energy of this invention is constituted by heat that is normally irreversibly discharged into the environment.
Engine intake air-enhancement-systems are normally characterized by centrifugal turbo-compressors, or turbo-chargers, and by positive displacement air compressors. The centrifugal compressors are devices utilized to provide excess air to the engine allowing increased power output and generally improving the combustion. These devices improve the overall engine efficiency because they recuperate a fraction of the kinetic energy and pressure energy contained in the exhaust gases produced during combustion. Centrifugal compressors are widely used in Internal Combustion (IC) engine applications since they show reasonably good efficiencies when they operate at the proper speeds, are reasonably rugged, and last for the entire life of the engine. Air compressors for IC engines are generally formed by two counter-opposed sections containing the Exhaust Gas Wheel, xe2x80x9cEGW,xe2x80x9d and the Compressor Wheel, xe2x80x9cCW,xe2x80x9d connected by a common shaft. The EGW converts parts of the kinetic and pressure energy of the exhaust gas into shaft power. Since the CW is also mechanically connected to the same shaft, it converts the shaft power provided by the EGW into air pressure at the discharge of the CW. In this manner, the engine intake manifolds become pressurized and more air/oxygen is available to the engine. Thanks to these devices, it is possible to increase the amount of fuel injected in the combustion chamber and increase the overall engine power output. Unfortunately, the efficiency of the centrifugal compressors is optimized only for a significantly high range of rotational speed of the CW (generally greater than 30,000 RpM). Such speeds are only reached when the mass of exhaust gases (mass flow rate, grams-per-second), matches the optimized EGW RpM, so that the maximum torque is transferred through the shaft to the CW. This unavoidable sequence of events creates the conditions for a delay, called xe2x80x9cturbo-lag,xe2x80x9d imposed mainly by the fluid-mechanical inertia of the exhaust gases, the mechanical inertia of the EGW, CW, and many other factors. Due to the fact that the exhaust gases are a consequence of the combustion process, the engine experiences a significant delay between the time the fuel is injected and the time the proper quantity of oxygen in the combustion chamber is made available by the compressor. This delay provokes a severe drop in engine performance during acceleration, particularly from idling to higher RpM. In fact, during these phases there is not enough oxygen to complete combustion, therefore the production of pollutant emissions is significant while the engine performance is impaired. This condition exists for several seconds every time the engine accelerates and it becomes even more pronounced when the engine is severely loaded.
Normally, if the engine is idling and the accelerator pedal is suddenly pressed the fuel appears inside the combustion chambers almost instantaneously, but the availability of oxygen is completely insufficient to complete combustion. Eventually, the engine RpM changes from idling to the desired speed and an increasing mass flow of exhaust gases starts to provide enough torque to the centrifugal compressor, thereby the availability of oxygen becomes gradually sufficient. In fact, as time passes the CW reaches the proper RpM and air is finally compressed inside the intake manifold. To summarize, during acceleration the conventional turbo compressors (centrifugal compressors in particular) are unable to provide oxygen to the engine for a time period depending on engine load and rate of acceleration. During this time a severe production of particulate (especially when heavy fuels are considered) is discharged into the environment. To eliminate, or minimize, the turbo-lag phenomena, some engine manufacturers utilize different mechanical compressors (i.e. positive displacement compressors) which show a reasonable efficiency at low RpM. These mechanical systems are coupled with the engine crankshaft, thereby utilizing power from the engine to operate (less efficient). When these devices are utilized the production of pollution is reduced during acceleration, but unfortunately engine performance is also penalized, especially at high engine RpM. The only commercial alternative widely used (for example for large diesel engines) is to utilize two different air-enhancing systems in tandem Therefore, a positive displacement air compressor, utilizing power from the engine, and a centrifugal compressor are coupled so that one provides oxygen at low RpM, while the other pressurizes the intake manifold at higher RpM. This solution is very expensive and results only in a modest improvement of the overall engine efficiency. Another way to provide excess oxygen inside the intake manifold at low engine RpM is represented by electrical compressor. These compressors are generally characterized by an electrical motor coupled with a centrifugal compressor able to provide excess oxygen to the engine independently of engine RpM. Generally, these electrical motors are controlled by sophisticated and expensive electronic controllers, and require extremely high current densities to provide the needed torque in a few hundreds of milliseconds. In other words, these compressors are capable of providing the needed oxygen at low engine RpM, but unfortunately they require extremely high electric consumption for their operation. The high current densities required for the electrical air compressors also poses serious problems by originating large emissions of electromagnetic interference, and by generally overloading the conventional electrical systems (i.e. alternator, batteries) aboard the vehicles. Therefore, although the electric compressors satisfy the requirement for oxygen at low engine RpM, they also require so much power to run that the overall energy balance might actually show a deterioration of the overall engine performance instead of the opposite.
The main objective of the proposed invention is to provide a waste energy recovery system capable of reducing environmental pollution while increasing the engine performance. Therefore, this invention converts heat into mechanical energy which can be used to produce electricity, air pressure, or availability of thermodynamic work.
One of the main objectives of the proposed invention is to provide an anti-pollution device while increasing the power system""s overall performance without affecting the fuel specific consumption. In general, this invention consists of a special thermodynamic engine coupled with the power system, the waste energy of which is the source of energy of the thermodynamic engine. Because the converters and expanders utilized are extremely compact, the overall MWHE can be easily assembled/integrated with a conventional IC engine. Superheated vapor is generated by injecting a relatively low-pressure fluid with the desired thermodynamic and thermal physical properties (i.e. water or any proper fluid) inside a special heat transfer converter which transfers the heat released by the cooling system and exhaust gases of the engine to the fluid instantaneously. In general, by considering a 50-60 horse-power (HP) engine, about 20-24 kW (where 1 kW=1.341 HP) are normally lost in the form of heat irreversibly discharged into the environment. This heat is normally lost through the exhaust gases and forced convection through the engine coolant system and radiator. The minimum energy required to accumulate enough oxygen inside the intake manifold when the engine is accelerating from idling to higher speeds can be estimated between 0.8-1 kW for a small volume engine, and about 3 kW for a medium large diesel-fueled engine. Normally the efficiency of a standard centrifugal air compressor is not greater than 60-70%, therefore the energy required at the compressor shaft is about 3.2 kW. A device utilizing a 20 kW energy source to convert it into 3.2 kW minimum energy required to provide compressed air should have an efficiency of at least 16%. Such a low efficiency is normally not even considered for power generation; however, in this case the energy source is waste energy and recuperating even a small fraction of it only represents a gain for the overall engine efficiency. Therefore, the thermodynamic cycle of the NWHE is a vapor cycle based on an injection of water (or a proper fluid) into the heat transfer converter which instantaneously flashes the water to superheated steam with no need for steam boilers or accumulation (as is for conventional vapor cycles). The pressure of the water injection and the mass flow rate can be varied as a result of the quantity of heat available inside the converter, or simply as a function of the amount of waste heat that we want to recuperate. Once water is injected inside the converter it expands instantaneously, changing its specific volume and making the heat transfer process extremely rapid. The energy collected by the superheated steam while transiting inside the converter is then utilized inside one or more expanders able to provide power directly to the crankshaft, and/or drive the oxygenators. If the engine is a medium-large volume engine the production of waste heat is greater than the heat necessary to only drive the oxygenators. In this case, the excess superheated steam energy can be utilized to drive an additional expander that returns (directly or indirectly) mechanical energy to the engine crankshaft. To summarize, the MWHE can be formed by one or more heat converters, and at least two expanders. One expander is coupled with the engine load through a special clutch, and the other provides a constant optimum speed for a special centrifugal-type compressor forming an air/oxygen enhancing system (oxygenator) powered by waste energy. The superheated steam formed inside the converter then expands in the expanders and condenses inside a radiator, or as a result of steam collapsing when exposed to the cold surfaces of chambers inside the expander (imploding systems). Furthermore, the sudden implosion of vapor inside the imploder chambers causes a drop in the system pressure (i.e. P=0.09 bar when T=45 C.xc2x0) which increases the efficiency of the MWHE thermodynamic cycle. At this point the condensed fluid (back in its liquid form) is pressurized back into the injector, and a new cycle starts over. By rough estimates, it is possible to assume that if the maximum temperature reached by the superheated steam inside the converter is only 450 C.xc2x0, the overall efficiency of the waste heat thermodynamic cycle is approximately 21%. This means that a vapor cycle with the above characteristics could provide at least 3.4 kW shaft power to a compressor of whatever type. In other words, the thermodynamic engine described in this invention can be utilized to power an air/oxygen enhancing system at no cost for the overall energy balance of the engine. If the converter provides a superheating temperature greater than 450 C.xc2x0, for example 600 C.xc2x0, the overall efficiency of the thermodynamic cycle would reach 29%. The maximum temperature achievable by the superheated vapor inside the converter is proportional to: the length of the converter: the distance between heated surfaces inside the converter; the roughness of the converter internal surfaces; mass flow rate of liquid fluid to be converted into vapor; mass flow rate of exhaust gases transiting inside the converter; thermal insulation between converter and surrounding environment; and many other less crucial variables. In general, exhaust gases temperatures can reach values higher than 600 C.xc2x0, and the relative efficiency of the converter can be much higher than 29%.
To summarize, the device of this invention recuperates a fraction of the energy normally lost in the form of heat from conventional power systems and combustion engines. By utilizing this energy to drive oxygen enhancing systems, engine pollution can be drastically reduced while engine performance is increased. By utilizing this same energy to drive a work-producing unit, the overall engine efficiency can be further improved since more power can be provided to the engine load. Then the overall engine power output is a result of the summation of the power normally provided by the engine and the power recuperated from the waste heat.